This invention relates generally to male molding members about which a material is formed. In particular, this invention relates to retractable mold protrusion assemblies in which the molding member is capable of retracting so that the molded part can be removed from the mold after being formed.
Items such as refrigerator or freezer door liners are normally shaped using a thermoforming process. Thermoforming consists generally of heating the material to be shaped until the material is sufficiently soft and plastic that it can be shaped. The material is then molded to the desired shape by applying pressure to the material around the mold form, or by drawing a vacuum.
It is common, especially for door liners, to have protrusions of different shapes and sizes extending from the side walls of the molded piece. In the case of refrigerator and freezer door liners, the protrusions are generally for hanging shelf trim or storage bins. After the door liner has been molded and has sufficiently cooled, molding protrusions, about which the protrusions in the door liner have been formed, must be retracted into the molding assembly so that the door liner can be removed from the mold. After the newly molded door liner or other part is cleared from the molding machine, the molding protrusions must return to their original protruding positions in order to form the next part.
It is typical in the industry for the molding protrusions to be operated by cylinders and linkages which hold the protrusion detail in place during forming and which retract the protrusion after the part has been formed to permit the molded part to be removed from the molding machine. This type of apparatus has suffered from the disadvantages of being relatively expensive to make and complex to operate, and is generally limited in its use to the specific machinery into which it has been incorporated. There is a need for a simpler device which is self-contained and self-operating, and which is easily interchangeable among various molding assemblies.